THIS invention relates to generator apparatus which can be used to supply loads which vary substantially with time.
In conventional electric generator sets an engine or other prime mover drives a synchronous alternator at a nominally constant speed which is calculated to provide an AC electrical output of the correct frequency. In practice, the engine speed does not remain exactly constant, with a resultant undesirable variation in the frequency of the electrical output of such generator sets.
In order to supply maximum load demand, such a generator set must be sized accordingly, which can be very wasteful due to the fact that the average load may typically be only 20% of the peak load. There are numerous applications, such as welding, battery charging and the starting/operation of electric motors where load demand may vary greatly, with only intermittent heavy loading of the generator set. Thus, it is desirable that a generator set which is used in such applications be able to cope efficiently with light load conditions.
Variable speed generator sets have been proposed (see, for example, U.S. Pat. No. 5,563,802 of Plahn et al) which respond to variations in load demand by varying the speed of the engine/generator, and which utilise batteries to supply the load under low-load conditions. However, known systems of this kind have various limitations, including a limited engine speed operating range, poor battery life due to onerous duty cycles, and poor performance under adverse load conditions.
It is an object of the invention to provide hybrid generator apparatus which can cope with substantial variations in load while also operating efficiently.